Fungal nail infection can make the nails thick, hard, discolored, brittle, painful, and eventually spread to other nails, including the thumb. Because nails grow slowly, it is rare for nail fungal infections to heal in a matter of weeks or months. Avoid wearing tight shoes, change your socks frequently, keep your nails dry and clean, and don't share shoes or nail cutters. Depending on the severity, doctors frequently employ antifungal medications like Terbinafine or antifungal nail paints or creams. However, treatment should be directed by a physician because certain medications may harm the liver or interfere with other medications. If the nail gets really painful or swollen, or if you have diabetes, please consult a dermatologist.